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Understanding how galaxies contributed to reionize the universe is one of the principal science goals of the James Webb space telescope (JWST). Because the IGM is neutral at high-redshift comma and therefore optically thick to ionizing radiation (LyC) comma JWST needs indirect LyC diagnostics calibrated on low redshift sources to unveil the sources of reionization. Here we propose the first sample selected based off their Mg II emission properties to have predicted LyC escape fractions. These 35 orbits of COS-HST observations will stringently test the best current LyC escape tracer in exactly the conditions that JWST will use it to infer the sources of cosmic reionization. Our mock JWST sample is completely different than any LyC sample as it is selected to have low neutral gas column densities. By comparing the Lyman Alpha and Mg II profiles we will understand the conditions when Mg II is optically thin and inform when JWST observations can use Mg II to measure the LyC escape fraction. The diverse physical properties of our sample and predicted LyC escape fraction will enable us to constrain the impact of dust and gas-phase metallicity in the inferred LyC properties. Two proposed targets are predicted to be extremely rare strong LyC emitters comma while being normal star forming galaxies. If confirmed comma these objects will provide a novel window into the escape of LyC. Beyond a simple test of confirmation comma we will treat these observations as if they were up-coming JWST observations to demonstrate whether future JWST observations can recover the LyC escape fraction.